The emerald ash borer, Agrilus planipennis Fairmaire, (Coleoptera: Buprestidae) is an invasive Palearctic species that has killed millions of ash trees (Fraxinus spp. L.) (Oleaceae) in the USA and Canada (Cappaert et al. 2005; Poland and McCullough 2006). Although initially detected near Detroit, Mich. in 2002, there is evidence that populations of this invasive species had been present in Michigan, USA and Ontario, Canada since the mid-1990s (Seigert et al. 2007). Since then, it has spread rapidly and has been detected in 15 states and two provinces, Ontario and Quebec, in Canada (EAB 2010). Movement of infested firewood and nursery stock has exacerbated its spread and large scale devastation of ash trees is predicted (Marchant 2006). Early detection of A. planipennis infestations has proven difficult because visual signs and symptoms, such as D-shape exit holes, epicormic shoots, bark deformities, and thinning crowns, usually appear only on heavily infested trees a year or more after populations have been established (Cappaert et al. 2005; de Groot et al. 2006, 2008; Poland and McCullough 2006). Development of a monitoring system is critical for early detection of A. planipennis populations, which would aid in management and control decisions. In order to maximize detection efficacy, a better understanding of the behavior and chemical ecology of adult A. planipennis is needed.
Adult A. planipennis are typically active between 0600-1700 h, particularly when the weather is warm and sunny (Yu 1992; Rodriguez-Saona et al. 2007), with mating occurring from 0900-1500 h and lasting for 20-90 min. Yu (1992) observed that adults preferred trees in open areas with direct sunlight and that during rainy or cloudy weather they tended to rest in cracks in the bark or on the foliage. Adult beetles, particularly males, spend much of their time in the canopy feeding and flying short distances (Lance et al. 2007; Lelito et al. 2007; Rodriguez-Saona et al. 2007). Indeed, traps in the mid-upper ash canopy capture more adults than traps hung below the canopy (Lance et al. 2007; Francese et al. 2007, 2008; Crook et al. 2008, 2009) and traps in locations exposed to direct sunlight (i.e. on the edge or near a gap) generally catch more adults than those in shaded locations (Poland et al. 2005; McCullough et al. 2006, 2009; Francese et al. 2008; Lyons et al. 2009).
Crook and Mastro (2010) reviewed the considerable progress made towards developing a trap that is effective at capturing A. planipennis (Francese et al. 2005, 2007, 2008, 2010; Crook et al. 2008, 2009; Lelito et al. 2007, 2008; McCullough et al. 2008). Color has been identified as an important factor affecting trap captures, with purple shown to be highly attractive (Francese et al. 2005, 2008; Crook et al. 2008). Purple traps typically catch more females than males (Francese et al. 2008; Crook et al. 2009), due to A. planipennis response to light in both the blue and red range of the visible spectrum (Crook et al. 2009). Currently, a sticky purple prism trap is utilized in surveys for A. planipennis in the United States (Francese et al. 2008; Crook and Mastro 2010). Adult A. planipennis also respond to green light in the 540-560 nm range of wave length 540-560 nm (Crook et al. 2009), with green traps capturing two to three times as many adults as purple traps. Crook et al. 2009 also found that dark green (24% reflectance) and light green (64% reflectance) caught more beetles than purple. Also, Francese et al (2010b) Can. Entomol. 142: 596-600 tested purple vs light green (540 nm, 64% reflectance) traps and reported that green caught more EAB, particularly males. Also, Francese et al. (2010a) J Econ Ent 103: 1235-1241 studied different green wavelengths and different reflectances, and concluded that the best trap would be a green trap with a wave length of 540 nm and 49% reflectance. Green traps typically have a bias towards males in trap captures (Lance et al. 2007; Rodriguez-Saona et al. 2007; Lelito et al. 2008; Crook et al. 2009). However, green traps typically catch more adults only when deployed high in the tree canopy. Thus, trap deployment, as well as color and lure combination, must be considered when evaluating traps for a monitoring program, as trap captures are likely influenced by adult preferences and behavioral activity patterns.
Numerous studies have described the chemical ecology of A. planipennis (Crook and Mastro 2010) and two types of host volatiles have been demonstrated to be attractive: bark sesquiterpenes (Poland and McCullough 2006; Crook et al. 2008) and green leaf volatiles (Poland et al. 2004, 2005, 2006, 2007; Rodriguez-Saona et al. 2006; de Groot et al. 2008; Grant et al. 2010). Girdled or stressed ash (Poland and McCullough 2006; Crook et al. 2008) are attractive to both sexes, as are Manuka and Phoebe oils which contain, in part, the sesquiterpenes emitted by stressed Fraxinus spp. (Crook et al. 2008; Crook and Mastro 2010; Grant et al. 2010). Of the green leaf volatiles, one compound in particular, (3Z)-hexenol, is highly antennally active and attractive to males (de Groot et al. 2008; Grant et al 2010). These results indicate that specific host volatiles act as kairomones in the chemical ecology of A. planipennis and these compounds may provide useful detection tools.
Much of the literature on the mating behavior of buprestids (e.g. Rodriguez-Saona et al. 2006; Lelito et al. 2007; Akers and Nielsen 1992; Gwynne and Rentz 1983; Carlson and Knight 1969) has described the use of visual and tactile cues for mate location. For buprestids, including those in the genus Agrilus, host location has been described as occurring first by olfactory processes and then mate location by visual, or by vibratory and/or tactile cues (Carlson and Knight 1969). However, Dunn and Potter (1988) showed attraction of A. bilineatus (Weber) males to cages containing females compared to host-logs only, suggesting the use of a female-produced pheromone.
Limited progress has been made into the pheromone chemistry of A. planipennis. Previous work suggested the presence of a contact pheromone (Lelito et al. 2007), subsequently identified by our research group as 9-methylpentacosane, which appears only on the cuticle of female A. planipennis at sexual maturity (7-10 d old) and stimulates full copulatory activity in males upon antennal contact (Silk et al. 2009), although 3-methyltricosane may also be involved as an additional component (Lelito et al. 2009). Bartelt et al. (2007) identified a volatile, antennally-active predominantly female-produced macrocyclic lactone, (3Z)-dodecen-12-olide [(3Z)-lactone], which was the first putative volatile pheromone described for A. planipennis, but no behavioral activity was reported.
Pureswaran and Poland (2009) reported that males were able to locate and identify females at close range using olfaction and an unidentified volatile cue. Here, we use GC-EAD in combination with field trapping and olfactometry to test whether (3Z)-lactone elicits behavioral responses in A. planipennis either alone or in combination with host kairomones (bark sesquiterpenes or green leaf volatiles). We tested various lure combinations on both purple and green traps, as both colors have been shown to be attractive. We also tested the lactone stereoisomer, (3E)-lactone, for its effect on A. planipennis behavior because preliminary studies suggested that exposure to UV-light catalyzes the isomerization of (3Z) to the (3E)-lactone and A. planipennis adults are known to favor sunny locations.